ABSTRACT. Stigma and discrimination relating to HIV/AIDS (?HIV-related stigma?) interfere with seeking and receiving appropriate treatment and care, contribute to depression, lower quality of life and other psychiatric disorders, and produce worsening clinical outcomes among people living with HIV/AIDS (PLWH). Despite global efforts to tackle HIV-related stigma for decades, HIV stigma remains a critical public health issue in US and globally, particularly in low and middle income countries including China. There are substantial knowledge gaps in our understanding of HIV-related stigma and underlying mechanisms through which the stigma negatively affected clinical outcomes of PLWH. Research has suggested both biological mechanism (e.g., increasing stress- related hypothalamic-pituitary-adrenal [HPA] activity) and behavioral mechanism (e.g., decreasing adherence to treatment and care) through which stigma may negatively impact clinical outcomes (e.g., CD4 counts, viral load, disease progression). However, these possible biological and behavioral mechanisms, while hypothesized, have not been empirically tested in longitudinal studies. In this US-China collaborative research project, investigators from University of South Carolina (USC) and Guangxi Provincial Center for Disease Control and Prevention (Guangxi CDC) propose a longitudinal epidemiological assessment among a cohort of 1,200 PLWH in Guangxi China where we have built a strong research infrastructure and community collaboration through NIH-funded research since 2004. The primary outcomes will be HIV clinical outcomes (CD4 count, viral load, disease progression) and the intermediate outcomes will include chronic stress response and adherence to treatment and care. In addition to self-reported data (e.g., depression and anxiety, adherence to treatment and care), biomarkers of stress (hair cortisol) and ART adherence (hair antiretroviral concentration) will be employed. The proposed research is designed to address one of the priority HIV/AIDS topic areas in RFA-AI-16-006 (i.e., ??studies focusing on reducing health disparities in the incidences of new HIV infections or in treatment outcomes of people living with HIV/AIDS?) and stimulate further collaborative research between US and Chinese investigators in the areas of HIV-related stigma and health disparities in treatment outcomes of PLWH.